' ValueError: too many values to unpack '

Question

I'm trying to write a basic version of minesweeper.You get the number of rows, columns,bombs and their location from the user. you should count number of bombs surrounding each element. consider the example below: input

4 3
5
1 1
4 3
1 3
4 2
3 2

output is:

* 2 *
2 3 2
2 * 3
2 * *

Here's my code:

n, m = [int(x) for x in input().split()]


k = int(input()) #number of bombs

#location of bombs
bomb = []
for i in range(k):
    r,c = [int(r) - 1 for r in input().split()]
    bomb.append([r,c])

#making the grid
map = []
for x in range(n):
    map.append([])
    for y in range(m):
        map[x].append(0)

#locate bombs       
for i, j in bomb:
    map[i][j] = '*'

#count the bombs
Ns = 0
for i, j in map:
    for x in range(-1, 2):
        for y in range(-1, 2):
            if map[i + x][j + y] == '*':
                Ns += 1

    map[i][j] = Ns

print(map)

My problem is finding bombs in surrendering. I get ValueError: too many values to unpack for line 25 . Any idea how can i fix it?

Answer 1

for i, j in map:

is invalid. map is a list of lists, something akin to a 4x3 array.

You seem to be trying to iterate through the indices of map , and have confused those with the list contents. Try

for i in range(len(map)):
    for j in range(len(map[i])):
        ...

Answer 2

There's two potential problems in your code.

Firstly, your map actually has 3 values to unpack for each value (since your m is 3), rather than two. This is the line that you need to fix:

for i, j in map:

Instead, what you need is probably to unpack each value for map, like so:

for x in range(len(map)):
    for y in range(len(map[i])):
        square = map[x][y]

Secondly, your code for checking the surroundings can run into issues because you simply decrement/increment the x and y of the mine by 1, this will make your code try to find indexes in the map that doesn't exist. Eg, if x is 2, incrementing by 1 will give you 3. breaking your list.

What you probably want is:

for i in range(max(0,x-1),min(x+1,n-1)+1):
    for j in range(max(0,y-1),min(y+1,m-1)+1):

This only takes in the values that are both in the surroundings, and do not violate the array bounds. Max(0, x-1) prevents us from giving negative array bounds, and min(x+1, n-1) prevents us from going over the max array bounds. Similarly so for y.

Combined, the code would probably look something like this:

#count the bombs
for x in range(len(map)):
    for y in range(len(map[i])):
        # if x,y is not a mine
        if map[x][y] != '*':
            # check the surroundings of x,y for mines
            Ns = 0
            for i in range(max(0,x-1),min(x+1,n-1)+1):
                for j in range(max(0,y-1),min(y+1,m-1)+1):
                    # if this surrounding block is a mine, add to Ns
                    if (map[i][j]) == '*':
                        Ns += 1
                        print("Not safe: " + str(Ns))
            # append the Ns number to the x,y block
            map[x][y] = Ns

for layer in map:
    print(layer)

Outputs:

['*', 2, '*']
[2, 3, 2]
[2, '*', 3]
[2, '*', '*']

Note that this is definitely not the most optimized solution for the problem; the best way is to save values as we go along so we don't have to check all the 3 to 8 surrounding tiles for every tile, but hopefully this helps you understand the base case for dealing with minesweeper.

Hope that helps!